Patent application title: PERISTALTIC HOSE PUMP

Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The invention concerns a peristaltic hose pump comprising a roller wheel
(1) rotatable about a roller wheel axis (D), which roller wheel has
rollers that are mounted thereon (2), the roller wheel rotation axes (R)
of which are arranged on a circle concentric with the roller wheel axis
(D), the rollers (2) partly projecting beyond the roller wheel (1),
comprising a hose (3), which has a flexible and elastic pump segment (4),
and the pump segment (4) being fixable in the axial direction at its two
opposite ends (5, 6) by means of one fixing point (P1, P2) each, and the
pump segment (4) being guided around the roller wheel (1) under elastic
tension, wherein the length (L1) of the pump segment (4) when not under
tension in proportion to the distance (A) of the fixing points (P1, P2)
to the roller wheel rotation axis (D) is adjusted with the provision that
while the roller wheel (1) is stationary and when applying a fluid
pressure in the range from 10 to 400 mbar to one end (P1, P2) of the pump
segment (4), a flow of the fluid of at least 0.01 1/min through the pump
segment (4) is obtained.

Claims:

1. A peristaltic hose pump comprising a roller wheel rotatable about a
roller wheel axis (D), which roller wheel has rollers that are mounted
thereon, the roller wheel rotation axes (R) of which are arranged on a
circle concentric with the roller wheel axis (D), the rollers partly
projecting beyond the roller wheel, comprising a hose, which has a
flexible and elastic pump segment, and the pump segment being fixable in
the axial direction at its two opposite ends by means of one fixing point
(P1, P2) each, and the pump segment being guided around the roller wheel
under elastic tension, wherein the length of the pump segment when not
under tension in proportion to the distance of the fixing points to the
roller wheel rotation axis is adjusted with the provision that while the
roller wheel is stationary and when applying a fluid pressure in the
range from 10 to 400 mbar to one end (P1, P2) of the pump segment, a flow
of the fluid of at least 0.01 1/min through the pump segment is obtained.

2. The peristaltic hose pump according to claim 1, wherein the distance
of at least one fixing point to the roller wheel axis is adjustable.

3. The peristaltic hose pump according to claim 1, wherein while the
roller wheel is stationary and when applying a fluid pressure in the
range from 10 to 300 mbar, preferably from 10 to 200 mbar to one end of
the pump segment, a flow of the fluid from 0.01 1/min to 1 1/min,
preferably to 0.5 1/min is obtained.

4. The peristaltic hose pump according to claim 1, wherein a bypass line
with a pressure-controlled bypass valve is arranged between the regions
of the ends of the pump segment.

5. The peristaltic hose pump according to claim 4, wherein the bypass
valve opens at a pressure from 100 to 500 mbar, preferably 200 to 400
mbar, most preferably 300 to 350 mbar.

6. The peristaltic hose pump according to claim 4, wherein the minimum
clear cross-section of the bypass line with opened bypass valve is 10 to
100%, preferably 20 to 50%, of the clear cross-section of the pump
segment when not under tension.

7. The use of a peristaltic hose pump according claim 1 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

8. The use of a peristaltic hose pump according to claim 7, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

9. The peristaltic hose pump according to claim 2, wherein while the
roller wheel is stationary and when applying a fluid pressure in the
range from 10 to 300 mbar, preferably from 10 to 200 mbar to one end of
the pump segment, a flow of the fluid from 0.01 1/min to 1 1/min,
preferably to 0.5 1/min is obtained.

10. The peristaltic hose pump according to claim 5, wherein the minimum
clear cross-section of the bypass line with opened bypass valve is 10 to
100%, preferably 20 to 50%, of the clear cross-section of the pump
segment when not under tension.

11. The use of a peristaltic hose pump according claim 2 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

12. The use of a peristaltic hose pump according claim 3 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

13. The use of a peristaltic hose pump according claim 4 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

14. The use of a peristaltic hose pump according claim 5 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

15. The use of a peristaltic hose pump according claim 6 for generating a
fluid flow through a medical instrument 11, wherein a fluid source is
connected at a feeding side of the hose, wherein the medical instrument
is connected at a pressure side of the hose, and wherein the roller wheel
is driven with a preselected and constant speed for feeding the fluid
from the feeding side to the pressure side.

16. The use of a peristaltic hose pump according to claim 11, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

17. The use of a peristaltic hose pump according to claim 12, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

18. The use of a peristaltic hose pump according to claim 13, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

19. The use of a peristaltic hose pump according to claim 14, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

20. The use of a peristaltic hose pump according to claim 15, wherein the
fluid source is a fluid container, which is arranged, preferably by 0.1
to 2 m, most preferably 0.1 to 1 m, above the higher end of the pump
segment, the fluid container communicating with the feeding side of the
hose without interposed pump.

Description:

FIELD OF THE INVENTION

[0001] The invention concerns a peristaltic hose pump, in particular for
use in the field of medicine, comprising a roller wheel, which can be
driven about a roller wheel axis, and which has rollers that are mounted
thereon, the roller wheel rotation axes of which are arranged on a circle
concentric with the roller wheel axis, the rollers partly projecting
beyond the roller wheel, comprising a hose, which has a flexible and
elastic pump segment, the pump segment being fixable in the axial
direction at its two opposite ends by means of one fixing point each, and
the pump segment being guided around the roller wheel under elastic
tension. The invention further concerns the use of such a peristaltic
hose pump for generating a fluid flow through a medical instrument.

BACKGROUND OF THE INVENTION AND PRIOR ART

[0002] Peristaltic hose pumps of the construction mentioned above are
known in various variants. There are in principle two basic concepts. The
first basic concept is that the hose arranged around the roller wheel is
pressed by means of a pressure arched element or the like against the
roller wheel. Such embodiments are for instance known from the documents
U.S. Pat. No. 4,798,580 and U.S. Pat. No. 5,044,902. The second basic
concept, on which the invention is based, consists in that the elastic
hose is pulled by a tensile force of suitable size with a sufficient
angle of wrapping, typically more than 90° and less than
270°, in most cases in the range from 150° to 220°,
around the roller wheel. Thereby, a pressure arched element or the like
is not necessary. The tensile force is dimensioned according to the
elastic properties of the hose such that in the region of a roller of a
roller wheel, the interior cross-section of the hose is reduced to
practically zero. By rotation of this region with the roller about the
roller wheel axis, the feed of the fluid in the hose is effected.
Examples are described in the documents U.S. Pat. No. 4,537,561 and U.S.
Pat. No. 5,213,483. A particularly advantageous variant of the second
basic concept is described in the document DE 199 60 668 A1.

[0003] It is common to all above peristaltic hose pumps that across a
broad range there is a nearly linear correlation between the speed of the
roller wheel and the flow, and in fact independently from the generated
pressure respectively counter-pressure. In these connections it is
however also known that with very high pressures respectively
counter-pressures, typically above 530 mbar, the correlation between
speed and flow becomes non-linear.

[0004] When using peristaltic hose pumps in the field of medicine, for
instance for generating a flow through a body cavity by introduction of a
medical instrument, which is fed by means of the peristaltic hose pump
with fluid, the pressure respectively counter-pressure is a critical
parameter. A doctor wishes on the one hand a high flow for rinsing the
body cavity. On the other hand, a certain pressure is in fact desirable
for expanding the body cavity, this pressure is however also a very
critical parameter. Approx. 500 mbar, better 400 mbar, should definitely
not be exceeded. Typical pressures, which are medically harmless, are in
the range from approx. 50 to 300 mbar.

[0005] For peristaltic hose pumps of prior art construction, comprehensive
safety measures are provided, in order to safely prevent an inadmissible
pressure rise in a body cavity when adjusting a high flow. Typically, a
pressure sensor is provided, which regularly monitors the pressure in the
body cavity and/or the feed line to the medical instrument respectively
the pressure side of the peristaltic pump and adjusts the drive of the
roller wheel to smaller speeds, if the pressure is too high. It is even
possible that the roller wheel is adjusted to reverse operation in the
case of a strong pressure rise in the body cavity. This will in
particular take place, when an inadmissibly high pressure could occur at
a very small flow already.

[0006] The above measurement and control measures are all in all
expensive, thus prior art peristaltic hose pumps being costly. It would
be desirable to provide a peristaltic hose pump for use in the field of
medicine, the roller wheel speed of which is preselectable and otherwise
constant, and in which a defined limit pressure cannot be exceeded for
any of the preselectable speeds, and in fact without the necessity of
suitable pressure sensors and control of the speed of the roller wheel.

TECHNICAL OBJECT OF THE INVENTION

[0007] It is therefore the technical object of the invention to propose a
peristaltic hose pump, which can be obtained in a simple construction, in
particular does not need measurements of the pressure in the body cavity
respectively on the pressure side of the peristaltic pump, nor control
measures for the drive of the roller wheel, and which nevertheless safely
excludes that a given maximum limit pressure is exceeded.

SUMMARY OF THE INVENTION AND PREFERRED EMBODIMENTS

[0008] For achieving this technical object, the invention teaches a
peristaltic hose pump comprising a roller wheel, which can be driven
about a roller wheel axis, and which has rollers that are mounted
thereon, the roller wheel rotation axes of which are arranged on a circle
concentric with the roller wheel axis, the rollers partly projecting
beyond the roller wheel, comprising a hose, which has a flexible and
elastic pump segment, the pump segment being fixable in the axial
direction at its two opposite ends by means of one fixing point each, and
the pump segment being guided around the roller wheel under elastic
tension, wherein the length of the pump segment when not under tension in
proportion to the distance of the fixing points to the roller wheel
rotation axis is adjusted with the provision that while the roller wheel
is stationary and when applying a fluid pressure in the range from 10 to
400 mbar to one end of the pump segment, a flow of the fluid of at least
0.01 1/min through the pump segment is obtained.

[0009] The roller wheel is typically set into rotation by means of an
electric motor drive, thereby the cross-section of the pump segment of
the hose being reduced in the region of a roller. The speed of the roller
wheel may be unregulated, for instance by applying a preselectable
voltage (for analogous electric motors) or frequency (for stepper motors)
to the electric motor drive. It is also possible to keep the speed of the
roller wheel constant at a preselectable speed by a control loop. Then, a
transducer, for instance a speedo dial, is typically arranged on the
shaft of the roller wheel, by means of which a speed signal is generated.
This speed signal is then compared in an analog or digital comparator
with a preselected nominal signal. When the speed signal indicates a too
low speed, compared with the nominal speed correlated with the nominal
signal, the comparator increases the voltage respectively the frequency,
which is applied to the electric motor drive. An essential element of the
invention is that this control or regulation does not obtain nor need as
input signal a signal of a pressure sensor arranged on the pressure side
of the peristaltic hose pump.

[0010] A pump segment of a hose is a partial length of the hose, which is
made of an elastic and flexible material. At the ends of the pump segment
respectively follow partial lengths of the hose, which in most cases, but
not necessarily are made of another material and/or are differently
dimensioned. The partial length of the hose, which forms the pump
segment, is limited and defined by the fixing points. The fixing points
are disposed in the geometric layout, related to directions orthogonal to
the roller wheel axis, at defined and fixed points in the peristaltic
pump. Thereby, the hose segment of a certain length is, after guiding it
around the roller wheel, under an elastic tension given according to the
length.

[0011] The invention is based first of all on the finding that the reason
for the non-linearity between speed and flow at high pressures is that
with very high pressures, the interior cross-section of the hose
respectively of the pump segment is reduced not to zero anymore in the
region of a roller of the roller wheel because of the (counter-)
pressure. Because of the pressure, there is therefore a backflow,
referred to the reduced interior cross-section of the pump segment and
the revolution thereof about the roller wheel axis, in opposition to the
direction of rotation of the roller wheel and consequently the feed
direction of the peristaltic hose pump. This backflow in turn is a
function of the pressure and becomes the higher, the higher the pressure
on the pressure side of the hose pump is.

[0012] The invention makes use of this finding for adjusting a maximum
attainable pressure in medically compatible pressure ranges, i.e., below
400 mbar, preferably below 300 mbar, by allowing the provision of a
backflow at normal operating conditions already. By the fact that even
while the roller wheel is stationary, a flow is already made possible, so
to speak a defined back flow leakage in the region of the reduced
interior cross-section of the pump segment in the region of a roller is
provided. This back flow leakage acts quasi as a bypass valve from the
pressure side to the feeding side of the hose.

[0013] By a peristaltic hose pump according to the invention, it is
achieved that with simplest design, namely without pressure-controlled
regulation of the roller wheel drive and without pressure measurement and
indication, nevertheless a hose pump for medical purposes meeting all
safety requirements is obtained. A peristaltic hose pump according to the
invention can thus be produced very cost-effectively. Further, its
handling is extremely simple, since an operator only needs to select a
defined speed, at which the roller wheel then constantly turns until
another preselection. Even with maximum preselected speed, exceedance of
a defined maximum admissible pressure value is inherently excluded.

[0014] Essential for the invention is the set-up of the length of the
elastic pump segment when not under tension in proportion to the distance
of the fixing points to the roller wheel rotation axis. In other words,
the set-up comprises the proportion of the length of the pump segment
when not under tension to the length of the pump segment when the pump
segment is guided under tension around the roller wheel by means of the
fixing points.

[0015] The set-up can in principle be provided in two different ways. On
the one hand it is possible to vary the length of the pump segment when
not under tension with fixing points being invariable with respect to the
roller wheel axis. By a test series with different lengths of the pump
segment when not under tension it can be tested, whether the flow
according to the invention is provided when the pump segment is guided
under tension around the roller wheel and while the roller wheel is
stationary. Alternatively, with invariant length of the pump segment, the
distance of a fixing point or the distances of both fixing points with
respect to the roller wheel rotation axis can be varied and adjusted in a
test series so that the flow according to the invention when the pump
segment is guided under tension around the roller wheel and while the
roller wheel is stationary. Depending on the employed hose material for
the pump segment and its dimensions, the provision according to the
invention can easily be adjusted by tests and assignment to the
respective constructional design of the pump segment.

[0016] In a peristaltic hose pump according to the invention, usually the
distance of the fixing points to the roller wheel rotation axis will not
be adjustable. Rather, regularly the length of the pump segment when not
under tension is adapted thereto in the above manner. For test purposes
respectively for the test series mentioned above of the second
alternative, it is however also possible that a peristaltic hose pump is
designed such that the distance of at least one fixing point to the
roller wheel rotation axis is adjustable.

[0017] For the purpose of a peristaltic hose pump according to the
invention, other hoses can also be used. With unchanged distance of the
fixing points to the roller wheel rotation axis, the length of the hose
segment has been determined and adapted in a corresponding way for every
type of a hose respectively hose segment. This may in particular have
been made for instance with a hose cassette according to the document DE
199 60 668 A1, to which herewith reference comprehensively is made.

[0018] Preferably, it is provided that while the roller wheel is
stationary and when applying a fluid pressure in the range from 10 to 300
mbar, preferably from 10 to 200 mbar to one end of the pump hose segment,
a flow of the fluid from 0.01 1/min to 1 1/min, preferably to 0.5 1/min,
most preferably to 0.1 1/min is obtained.

[0019] Alternatively respectively preferably, the set-up of the length of
the pump segment when not under tension in proportion to the distance of
the fixing points to the roller wheel axis is made with the provision
that with maximum speed of the roller wheel and closed pressure side of
the hose, a pressure of not more than 500 mbar, preferably of not more
than 450 mbar, most preferably not more than 400 mbar, in particular not
more than 350 mbar or 300 mbar, appears on the pressure side. In addition
to this, an optimization of the flow can also simultaneously be made such
that with the above maximum pressures a maximum flow, for instance of
more than 0.6 1/min, preferably more than 0.7 1/min, most preferably more
than 0.8 1/min, in particular more than 0.9 1/min, for instance more than
1.0 1/min, is achieved.

[0020] As an additional safety measure against inadmissibly high
pressures, a bypass line with a pressure-controlled bypass valve can be
arranged between the regions of the ends of the pump segment. The bypass
valve can open at a pressure from 100 to 500 mbar, preferably 200 to 400
mbar, most preferably 300 to 350 mbar. The clear cross-section of the
bypass line with opened bypass valve can be 10 to 100%, preferably 20 to
50%, of the clear cross-section of the pump segment when not under
tension. The clear cross-section is the total passage area for the fluid.

[0021] Typically the following materials can be used for the pump segment:
elastomeric silicone polymers, soft PVC or similar materials, which are
known to the man skilled in the art. Typical inner diameters are in the
range from 6 to 10 mm, preferably 7 to 9 mm, for instance 8 mm. Typical
wall thicknesses are in the range from 1 to 2 mm, for instance 1.5 mm.

[0022] The invention also concerns the use of a peristaltic hose pump
according to the invention for generating a fluid flow through a medical
instrument, wherein a fluid source is connected at a feeding side of the
hose, wherein the medical instrument is connected at a pressure side of
the hose and wherein the roller wheel is driven with a preselected and
constant speed for feeding the fluid from the feeding side to the
pressure side. For the preselection, typically a rotary switch or a key
pad can be provided, and to each switch position respectively each key, a
defined constant speed of the roller wheel is assigned, and the electric
motor drive of which is correspondingly controlled. Instead of a rotary
switch, a continuous control element, such as for instance a
potentiometer, can also be provided. Of course, a digital entry
respectively preselection of the speed by means of an input field is also
possible.

[0023] Preferably, the fluid source is a fluid container, which is
arranged, preferably by 0.1 to 2 m, most preferably 0.1 to 1 m, above the
higher end of the pump segment, the fluid container communicating with
the feeding side of the hose without interposed pump. The hose pump acts
quasi as a booster for the hydrostatic pressure resulting from the
arrangement of the fluid container. Compared to the classic bag
suspension and height adjustment without pump, an increased flow through
the medical instrument achieved being often medically desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following, the invention is explained in more detail with
reference to figures representing an example of execution only. There
are:

[0025] FIG. 1: a schematic view of a peristaltic hose pump according to
the invention, and

[0026] FIG. 2: the arrangement when using a peristaltic hose pump
according to the invention in the field of medicine.

DETAILED DESCRIPTION

[0027] In FIG. 1 it can first be seen that the peristaltic hose pump
comprises a roller wheel 1 which can be driven about a roller wheel axis
D, said roller wheel 1 having rollers 2 that are mounted thereon, the
roller wheel rotation axes of which R being arranged on a circle
concentric with the roller wheel axis D, the rollers 2 partly projecting
beyond the roller wheel 1. The roller wheel axis D and the roller wheel
rotation axes R extend in parallel to each other. For reasons of clarity,
the electric motor drive of the roller wheel is not shown, which is
supplied with preselectable operating voltages. For this purpose,
suitable power supply circuits are provided.

[0028] Furthermore, a hose 3 is provided, which has a flexible and elastic
pump segment 4, in the embodiment made of an elastomeric silicone
polymer. The pump segment 4 is fixed at its two opposite ends 5, 6 in the
axial direction, referred to the pump segment, by means of one fixing
point P1, P2 each. The fixing points P1, P2 can allow a rotation of the
end of the pump segment 4 about an axis orthogonal to the axial direction
of the pump segment 4.

[0029] In the representation of FIG. 1, the pump segment 4 is shown in
mounted condition, i.e. guided under elastic tension around the roller
wheel 1 and when under tension. When under tension, the pump segment 4
has the length L2. When not under tension, i.e. not guided around the
roller wheel 1, the pump segment 4 has a length L1 (not shown). The
length L1 is smaller than the length L2. The length is herein the
longitudinal extension of the center axis through the pump segment 4.

[0030] The length L1 of the pump segment 4 when not under tension is
adjusted in proportion to the distance A of the fixing points P1, P2 to
the roller wheel axis D respectively to the length L2 with the provision
that while the roller wheel 1 is stationary and when applying a fluid
pressure in the range of 100 mbar to one end P1, P2 of the pump segment
4, a flow of the fluid of approx. 0.3 1/min through the pump segment 4 is
obtained.

[0031] For adjusting the above provision respectively for carrying-out
test series for determining the suitable length L2, the distance A of one
or both fixing points P1, P2 to the roller wheel rotation axis D can be
adjustable. Usually, however, the distance A will not be adjustable, and
the length L1 of the pump segment 4 has been adapted correspondingly in
previous tests.

[0032] Furthermore, it can be seen in FIG. 1 that a bypass line 7 with a
pressure-controlled bypass valve 8 is arranged between the regions of the
ends 5, 6 of the pump segment 4. The bypass valve 8 opens at a pressure
of approx. 300 mbar. By means of the bypass line 8 and the bypass valve
8, if applicable an additional backflow for the pressure relief of the
pressure side 10 is provided. The bypass valve 8 may be carried out in
most various ways. In the simplest case, it is a pressure-dependant
mechanical control element, having a valve seat and a spring-loaded
closing element that without any further control from outside opens
against the spring force or closes with the spring force. By pressure
application to the closing element, the latter will be moved against the
spring force, when a predetermined maximum pressure value defined by the
spring force is exceeded, and will come free from valve seat, so that
fluid can drain respectively flow back from the pressure side through the
bypass valve 8. Alternatively, the bypass line 7 may be a flexible hose,
which extends in a clamping element. Such a clamping element comprises a
supporting surface, against which the bypass line 7 rests, and a clamping
actuator, which for instance can be driven by an electric motor, and
which is pressed on the bypass line 7 on the side of the bypass line 7
opposite to the supporting surface and compresses the bypass line 7
against the supporting surface. Thereby, a continuous variation of the
flow cross-section through the bypass line 7 and thus a continuous
variation of the pressure can be obtained.

[0033] In FIG. 2, the use of the peristaltic hose pump according to the
invention for generating a fluid flow through a medical instrument 11 is
shown. At the feeding side 9 of the hose 3, a fluid source 12 is
connected. At the pressure side 10 of the hose 3, the medical instrument
11 is connected, the end of which can for instance be introduced into a
not shown body cavity. The roller wheel 1 is driven with a preselected
and constant speed for feeding the fluid from the feeding side 9 to the
pressure side 10. For preselecting the desired constant speed, a rotary
switch 13 is provided. Of course, instead of a rotary switch 13, a
continuously operating actuator can also be provided. In FIG. 2 it can
further be seen that the fluid source is a fluid container 12, which is
arranged approx. 1 m above the end 6 of the pump segment 4. Between the
fluid container 12 and the feeding side 9 of the hose 3, there is no pump
or the like interposed.

[0034] In particular in FIG. 2 can be seen that a peristaltic hose pump
according to the invention basically effects an increase of the
hydrostatic pressure provided by the fluid container 12.

[0035] In the following, a test series for determining a suitable length
L2 is described. For this purpose, a peristaltic hose pump of the basic
design of FIG. 1 was used. By a manually operated spindle drive, the
distance A of the two fixing points P1, P2 could be varied. A change of
the distance A therefore corresponds to a change of the length L2 by
twice the change of the distance A. Besides that, it is a standard hose
pump and a standard pump segment 4.

[0036] The measurements were made with a structure according to FIG. 2 by
means of a standard instrument as medical instrument, which was
introduced into a dummy representing a body cavity. The dummy comprised
an outflow cock. First, the flow with opened outflow cock was measured.
Then the outflow cock was closed, and the resulting pressure in the dummy
was measured. The fluid container was arranged at a level of approx. 1 m
above the fixing point P1. The dummy was approx. at the level of the
fixing point P1. The data in Table 1 were obtained.

[0037] The parameter A is given in arbitrary relative units. Speed is the
speed of the roller wheel. Graviflow designates the flow while the roller
wheel is stationary. Flow indicates the maximum flow with opened outflow
cock. Pressure in the dummy indicates the maximum pressure in the dummy
with closed outflow cock. The values in parentheses are measured values
that were taken again after 2 hours elapsed.

[0038] It ca be seen that for A=-2, 0 and 2, the roller wheel 1 does not
seal the pump segment 4. For A=-2, the attainable flow is relatively low.
For A=0, the attainable flow is satisfactory. For A=-2 and 0, there are
no maximum pressures of more than 400 mbar. The optimum adjustment is
therefore A=0.